Objective To analyze the ecological surveillance results of Aedes vector in 12 provinces (autonomous regions or municipalities) in China in 2020-2021, and to provide a scientific basis for risk assessment, prediction, early warning, and control of Aedes-borne diseases. Methods The surveillance data of larval and adult Aedes densities at the special investigation sites of Aedes vector in 12 provinces (autonomous regions or municipalities) in China were collected and statistically analyzed by SPSS 18.0 software. Results In 2020-2021, the mean Breteau index (BI) was >10.00 in Hainan, Zhejiang, and Hunan provinces and >5.00 in Guangxi Zhuang Autonomous Region (Guangxi) and Yunnan, Henan, and Shandong provinces. The mean mosq-ovitrap index (MOI) was >5.00 in Guangxi, Guangdong, Hainan, and Shandong. The mean net trap index was ≥2.00 mosquitoes/net·hour in Henan, Hubei, and Shandong and >1.00 mosquito/net·hour in Guangxi, Guangdong, Hainan, Yunnan, Fujian, and Hunan. There were no statistical differences in BI, MOI, and net trap index between class I provinces (Guangdong, Hainan, Guangxi, Fujian, Yunnan, and Zhejiang) and other classes of provinces (t=0.766, 1.030, and -0.745, all P>0.05). The mean BI in 2020-2021 was higher than that in 2017-2019 in Guangdong, Guangxi, Yunnan, and Shandong, but lower than that in the three years in other provinces. The Aedes vector was found to be active throughout the year at the investigation sites in Guangdong, Hainan, Guangxi and Yunnan, from March to December in Fujian, Zhejiang, and Hubei, and from April to November in Chongqing municipality, Shandong and Henan, and from April to December in Jiangxi. The results of BI and MOI were inconsistent in Yunnan, Guangxi, and Hubei. During the study period, the BI of Aedes vector was >5.00 in areas where dengue outbreaks and local cases occurred, and >10.00 in Ruili city in Yunnan, Cenxi city of Wuzhou in Guangxi, and Sanjiao town of Zhongshan in Guangdong; the net trap index in Cenxi city of Guangxi was >2.00 mosquitoes/net·hour. Conclusion In 2020-2021, the mean Aedes density in the provinces with local cases of dengue fever in China was high, with spatio-temporal heterogeneity among different regions. It is suggested that in the local transmission areas of dengue in China, it is necessary to adjust moderately annual surveillance periods, to continuously strengthen Aedes vector surveillance and risk assessment, and to systematically sort out the ecological investigation results of Aedes vector, so as to provide a scientific basis for the revision and improvement of Aedes vector surveillance scheme and the outbreak control of Aedes-borne diseases in China.

Objective To analyze the ecological surveillance data of Aedes albopictus, the dengue vector, in Shandong province, China in 2020, and to provide a scientific basis for effective prevention and control of dengue fever. Methods From April to November 2020, Ji’nan, Qingdao, Zibo, Yantai, Jining, Tai’an, Liaocheng, and Heze were selected from the whole province as surveillance sites. The Breteau index (BI) method was used to monitor mosquito larvae, and the double-layered mosquito net method was used to monitor adult mosquitoes. Excel 2010 software was used for data colletion, and SPSS 19.0 software was used for data analysis. The Chi-square test was used to analyze the differences in Aedes vector breeding among various habitats and standing water types. Results In 2020, the mean BI of Ae. albopictus in Shandong province was 9.64, and the mean net trap index was 2.58 mosquitoes/net·hour. In terms of habitat types, urban residential areas had the highest BI (12.22), and used tire dumping grounds/waste stations/construction sites had the highest net trap index (3.59 mosquitoes/net·hour). Both mosquito surveillance methods showed that the density of Ae. albopictus was relatively high from early July to late September. The positive results of the BI method first appeared in late April; BI reached the highest value (27.17) in mid-August and became 0 in late November. The positive results of the double-layered mosquito net method first appeared in mid-May; the net trap index reached the highest value in early August and became 0 in early November. In terms of standing water types, basements/garbage in parking lots and green belts/small puddles had the highest positive rate of Aedes mosquitoes. The eight monitoring sites in Shandong province had different Ae. albopictus densities. Liaocheng had the highest BI (19.60) and Yantai had the lowest BI (1.47). Tai’an had the highest net trap index (8.91 mosquitoes/net·hour) and Heze had the lowest value (0.29 mosquitoes/net·hour). Conclusion The density of Ae. albopictus is high in Shandong province from early July to late September. It is necessary to strengthen the mosquito control in residential areas and used tire dumping grounds/waste stations/construction sites. Basements/garbage in parking lots and green belts/small puddles are important breeding sites for Ae. albopictus. People in areas with high surveillance density of Ae. albopictus should raise awareness and take timely measures to reduce the risk of local dengue outbreak.

Objective To investigate the population density and seasonal variation of Aedes albopictus larvae in dengue prone and risk areas of Zhejiang province, China, 2020, and to provide basic data for the surveillance, prevention, and control of dengue fever. Methods Six surveillance sites were selected based on the presence or absence of local dengue fever cases in the past. In April to December 2020, mosq-ovitrap and Breteau index (BI) were used to monitor the population density of Ae. albopictus every 10 days of each month; Excel 2010 software was used for data arrangement, and GraphPad Prism 6 software was used to analyze the difference and correlation between mosq-ovitrap index (MOI) and BI. Results The mean MOI was 4.75, and the positive mosq-ovitraps containing both eggs and larvae had the highest proportion of 45.52%; the surveillance sites with local dengue fever cases in the past had a significantly higher MOI than those without local cases (5.72 vs. 3.73, χ²=64.050, P <0.05). The mean BI was 11.64, and idle containers (bowls, bottles, jars, and tanks) had the highest proportion of 56.13%; the surveillance sites with local dengue fever cases in the past had a significantly higher BI than those without local cases (15.54 vs. 7.63, χ²=391.800, P<0.05). MOI was positively correlated with BI in rural residential areas (r=0.739, P<0.05), while there was no statistical correlation between MOI and BI in urban residential areas (r=0.499, P=0.171). Conclusion There is a risk of dengue fever transmission in April-November in Zhejiang province, and the investigation results show that both MOI and BI can reflect the population density of Ae. albopictus larvae, which can be used to monitor the population density of dengue vector Aedes.

Objective To investigate the dengue vector Aedes density and seasonal fluctuation in Nanning, Beihai, Qinzhou, and Baise, Guangxi Zhuang Autonomous Region, China, and to provide a strong basis for the scientific prevention of dengue fever. Methods According to the "Special investigation of dengue vector Aedes" issued by Chinese Center for Disease Control and Prevention, the Breteau index (BI) method, the mosq-ovitrap index (MOI) method, and the double-layered mosquito net method were used to monitor the density of larval and adult Ae. albopictus mosquitoes in 2020-2021. ArcGIS 10.5 software was used to plot the spatial distribution of surveillance sites of vector Aedes. SPSS 16.0 software and the one-sample t-test were used to perform the statistical analysis. Results In 2020-2021, the overall mean BI, MOI, and net trap index at all surveillance sites were 10.83, 9.39, and 2.04 mosquitoes/net·hour, respectively. According to the statistical analysis, At most surveillance sites, there were statistical differences between BI and the overall mean BI (all P<0.05), between the net trapping index and the overall mean net trap index (all P<0.05). At half of the surveillance sites, there were no statistical difference between MOI and the overall mean MOI (all P>0.05). The BI at all surveillance sites was higher than 5.00 from March to November, and reached the peak value (16.73) in August. The MOI at all surveillance sites was higher than 5.00 from April to October, and reached the peak value (20.86) in July. The net trap index at all surveillance sites was higher than 2.00 mosquitoes/net·hour from May to September, and reached the peak value (4.57 mosquitoes/net·hour) in July. Conclusion The density of Aedes mosquitoes in Guangxi Zhuang Autonomous Region is at a relatively high level. The results suggested it is urgent to carry out the prevention and control of adult Aedes mosquitoes from July to August and the breeding sites cleaning of Aedes larvae from August to September, so as to control the mosquito density below the safety threshold and reduce the risk of dengue outbreak.

Objective To investigate the resistance level of Aedes albopictus against some commonly used insecticides in dengue endemic provinces of China, and to provide guidance for the proper usage of insecticides and epidemic prevention and control. Methods Excel 2016 software was used to collect and sum up the bioassay data of Ae. albopictus resistance to commonly used insecticides from 80 surveillance sites in 13 provinces in China. The WHO tube method was used to monitor the resistance of adult mosquitoes against 9 insecticides, and larval dip method was used to monitor the resistance of larvae mosquitoes against 3 insecticides. According to the Implementation Plan for National Vector Surveillance (2016), the resistance level was statistically analyzed and mapped using ArcGIS 10.3 software. Results The resistance of Ae. albopictus was monitored at 80 surveillance sites in China in 2020. For pyrethroid insecticides, Ae. albopictus adults developed resistance to deltamethrin, permethrin, beta-cypermethrin and beta-cyhalothrin at 83.08% (54/65), 77.97% (46/59), 87.30% (55/63),and 79.31% (46/58) of the surveillance sites, respectively. For carbamate insecticides, Ae. albopictus adults developed resistance to propoxur in 1.49% (1/67) sites, while none of the 61 sites showed resistance to bendiocarb. For organophosphorus insecticides, the Ae. albopictus adults at the 6.45% (4/62) surveillance sites developed resistance to malathion, while the 52 and 59 sites did not develop resistance to fenitrothion and chlorpyrifos. Ae. albopictus larvae at 93.48% (43/46), 28.30% (15/53), and 25.45% (14/55) of the sites showed medium or high resistance to pyriproxyfen, propoxur and temephos, respectively. Conclusion The resistance level of adult Ae. albopictus to pyrethroid insecticides and larva to pyriproxyfen were serious in dengue endemic and risk areas in China. However, both adult and larva were more susceptible to carbamate and organophosphorus insecticides at most of surveillance sites. Local authorities and program managers should adjust their insecticide use planning for Aedes mosquito control and dengue prevention and control according to the current insecticide resistance status.

Objective To investigate the population density and insecticide resistance of dengue vector Aedes in Yunnan border region of China, and to provide a scientific basis for rational use of insecticides to control dengue fever. Methods In 2020, Breteau index (BI) method was used to monitor the population density of dengue vector Aedes in residential areas of Ruili, Gengma, Mengla, Lancang, Hekou, and Mangshi in Yunnan border region, at a frequency of once a month in January-April and December and twice a month from May to November; the adult mosquito contact tube method was used to detect the resistance of adult Ae. aegypti and Ae. albopictus to nine insecticides, i.e., lambda-cyhalothrin, deltamethrin, beta-cypermethrin, permethrin, propoxur, bendiocarb, fenitrothion, malathion, and chlorpyrifos. Results Aedes larvae were active all year round at the field investigation sites, with the peak of BI in July-September; Of the six border counties and county-level cities, Ruili city had the highest mean BI of 15.62 and Mangshi city had the lowest mean BI of 3.03. Both Ae. aegypti and Ae. albopictus reached resistance level to lambda-cyhalothrin and permethrin and were sensitive to bendiocarb, malathion, and chlorpyrifos. Conclusion There is a high population density of dengue vector Aedes in Yunnan border region, and they have developed resistance to both lambda-cyhalothrin and permethrin. It is suggested that relevant departments should strengthen the surveillance of the density and insecticide resistance level of dengue vector Aedes larvae and guide the rational use of insecticides to slow down the development of insecticide resistance.

Objective To investigate the resistance of Aedes albopictus to commonly used insecticides, after control of a dengue fever outbreak in Chongqing, China, 2019, and to provide a basis for controlling mosquito-borne diseases including dengue fever and Aedes vector. Methods From May to October, 2020, Ae. albopictus mosquitoes were collected from parks or waste tire piles in 6 districts (counties) of Chongqing and were reared for 1-2 generations in laboratory, and the larval dipping method and the adult exposure tube method were used for insecticide resistance surveillance. Results Ae. albopictus larvae from each investigation site of Chongqing had varying degrees of sensitivity to commonly used insecticides, with a resistance ratio of 0.46-7.32. The resistance ratio was 0.46-4.92 for temephos and 0.82-7.32 for propoxur. Adult Ae. albopictus mosquitoes from each investigation site of Chongqing developed varying degrees of resistance to deltamethrin, permethrin, beta-cypermethrin, and lambda-cyhalothrin, with a 24-hour death rate of 5.88%-78.22%. The adult Ae. albopictus mosquitoes in the field of Wanzhou district developed suspected resistance to bendiocarb and fenitrothion, and those in the field of Dazu district developed suspected resistance to chlorpyrifos; the adult Ae. albopictus mosquitoes in the field of the remaining investigation sites were sensitive to propoxur, bendiocarb, malathion, fenitrothion, and chlorpyrifos. Conclusion Ae. albopictus adult mosquitoes from each investigation site of Chongqing develop resistance to pyrethroids, and Ae. albopictus larvae from some investigation sites develop a low level of resistance to temephos and propoxur. It is recommended to regularly monitor the resistance level and changing trend of Ae. albopictus and to select corresponding insecticide use strategies according to the insecticide resistance of Ae. albopictus at different developmental stages.